1. Field of the Invention
The present invention relates to an apparatus for recording and reproducing information by reciprocally driving a record medium relative to a head, and more particularly, to an information recording and reproducing apparatus having means for controlling a drive speed of a medium.
2. Related Background Art
Magnetic and optical apparatus have been known as information recording and reproducing apparatus which records and reproduces information by reciprocally driving an information recording medium relative to a head. In addition, the optical apparatus has been recently particularly noticed.
The recording medium of the optical information recording and reproducing apparatus which records and reproduces information by using a light beam includes the disk-shaped optical disk, card-shaped optical card and optical tape. These have respective features and are selectively used depending on the object and application. Among others, the optical card has a wide application because of its ease of manufacture, portability and accessability.
Various means for scanning the optical card by a light beam are known. A method of reciprocally and linearly moving the record medium relative to the light beam and relatively moving the beam irradiation position orthogonally to the direction of the reciprocal movement is simple in construction and assures a high precision.
FIG. 1 shows a schematic construction to illustrate control of the reciprocal movement of the optical card in the prior art optical information recording and reproducing apparatus.
In FIG. 1, a card C is reciprocally driven in a direction of extension of an information track T by a belt 2 and pinch rollers 3 and 33 as a motor 1 rotates. The right edge and left edge of the driven card C are detected by edge detectors 4 and 5, respectively. The motor 1 is provided with an encoder 6 for detecting speed, and an output thereof is applied to a frequency-voltage converter (FVC) 7 which converts a pulse signal representing a rotation speed of the motor 1 to a voltage signal. An error signal between the detected speed and a target speed is produced, amplified by an amplifier (AMP) 8 and then supplied to a loop filter 9, an output of which is supplied to a motor driver 11 through polarity inverter 10. The motor driver 11 supplies a drive current to the motor 1 to control the rotation speed of the motor 1. The inverter 10 switches a polarity of the voltage in accordance with the drive direction of the motor 1 in response to a command from a main control circuit 13 sent through an interface 12. In this manner, a drive servo is constructed.
When the detector 4 or 5 detects the right or left edge of the card C, information is sent to the main control circuit 13 through the interface 12. The main control circuit 13 decodes the information and commands the drive direction of the motor 1 to the inverter 10 through the interface 12, commands switching of the gain of the amplifier 8 to a gain switching circuit 14, and command switching of a time constant of the FVC 7 to a time constant switching circuit 15. The drive control of the optical card is disclosed in copending U.S. Pat. Application Ser. No. 07/213,515 filed on June 28, 1988.
Data is recorded on the card C by modulating a laser diode in an optical head 16 in accordance with data sent from a record data source (not shown) to the optical head 16, and scanning a medium surface of the card C by a laser beam emitted from the laser diode. The data is reproduced by scanning the card C by a non-modulated laser beam and detecting reflected light by a photo-detector in the optical head 16. The optical head 16 is moved transversely to a track T by a stepping motor (not shown) to record and reproduce information on and from different tracks. The drive speed of the medium in a playback mode is usually faster than that in a record mode, as disclosed in U.S. Pat. Application Ser. No. 936,599 filed on Dec. 1, 1986, now U.S. Pat. No. 4,831,243.
One of the disadvantageous features of the apparatus is a fluctuation of the movement speed which causes nonuniform bit interval of the recorded data and reduces reliability in recording and reproducing information on and from the card. As a result, a high precision speed control is required by a card feed control system. However, in the prior art apparatus, it is difficult to control the speed with high precision in the record mode when the medium is driven at a relatively low speed.
As another speed control method, a phase locked loop (PLL) method in which an output from an encoder is phase-compared with a reference clock and a phase error is fed back to a motor, has been known. This method is disclosed in detail in U.S. Pat. No. 4,330,196 (May 18, 1982) and U.S. Pat. No. 4,639,649 (Jan. 27, 1987).
An advantage of the PLL system is a very high precision speed characteristic for a small mechanical load variation. On the other hand, it has a disadvantage that the distance and time required for phase lock and stabilization since the start of movement are long. Thus, the problem is minor when the motor is continuously rotated in one direction, but when the card is reciprocally moved at a high speed in the information recording and reproducing apparatus, astable speed areas occur at the opposite ends of the card, that is, the start-up area and braking area are long and an effective data record area is narrowed.